Load-supporting pallets adapted to be handled by forklift trucks are well known in the art and many enjoy substantial commercial usage. Further, various specialized pallet configurations have been evolved over the years by different industries.
Preferable materials of construction for pallets have traditionally been steel or wood. Wooden pallets were at one time advantageous because of their comparatively low initial cost and low density. There are a number of drawbacks, however, to the use of wooden pallets, particularly in the realm of economics and practicality. From a practical standpoint, wooden pallets are quite difficult to maintain and after a period of time, are rendered ineffective for use when subjected to normal abuse in the trade. Furthermore, when the wooden pallets are used in a normally humid atmosphere or in a location where they are subjected to contact with liquid substances, the wood can rapidly deteriorate. The wooden pallets can therefore have a shorter life than pallets formed of other materials.
Many problems are inherent in the use of wooden pallets in a wide variety of applications. The wooden pallets are constructed by placing the frame members and cover boards in the desired locations and securing the same by means of nails or staples. After some use, however, these metal securement means are ultimately urged out of their point of securement thereby rendering the pallet defective. Vibration, which often results from carrying the pallets on a moving vehicle, causes the nails or other metal fasteners to work out of their fastening positions. Furthermore, the wooden pallets have a substantially greater weight than, for example, a plastic pallet constructed of substantially equal size. Consequently, freight costs are higher when wooden pallets are employed over plastic counterpart pallets.
There has been a recent introduction in the marketplace of pallets formed primarily of plastic materials. These pallets, however, like their wooden counterparts, also suffer from a number of disadvantages. The plastic pallets must include an upper load-supporting surface and a bottom loadsupporting, surface, the latter being provided with some means for contacting the floor or other supporting structure. These two substantially horizontal surfaces must be supported in some fashion to maintain rigidity especially when loaded. The pallets generally include some type of internal rib structure, lattice or web structure to maintain the spacing between the two walls and to provide internal strength. The presently available techniques used in the making of the pallets reside in rotational molding, extrusion blow molding or thermoforming. With the exception of rotational molding, however, molds necessary to produce structures of this type are quite expensive. In many cases, the processes for producing these pallets result in a substantial cost which does not afford any significant economic advantage over wooden pallets.
U.S. Pat. No. 3,667,403 issued June 6, 1972 discloses a two-piece plastic pallet which is said to provide improved properties. The pallet is formed by securing two mating unitary plastic members by means of bolts or other fasteners. The upper and lower surfaces of the assembled pallet have a plurality of apertures extending vertically through the assembly. Such a plastic pallet assembly is clearly unsuited for transporting bulk loads of powdered chemicals and the like.
U.S. Pat. No. 3,563,184 discloses a molded plastic pallet with a top surface disposed over a lower support surface. The two parallel, spaced surfaces are connected and reinforced by rows of aligned apertures and circular webs.
U.S. Pat. Nos. 3,511,191 and 3,140,672 both disclose unitary molded pallets having smooth, continuous upper decks and reinforced lower decks with hollow support legs depending from the lower deck but integrally formed with the pallet.
Providing a unitary plastic pallet light in weight, durable, easily cleaned, nestable, capable of directly supporting heavy powder loads and capable of four-way entry with forklift equipment constitutes one of the principal objects of the present invention. Another object is to provide a pallet of the aforementioned type which is particularly adapted to fluidized bed operation with powdered materials. Still another object is to provide a unitary plastic pallet wherein the upper and lower decks are not joined together with fastening means.